This application claims the priority of German patent document 198 06 423.3, filed Feb. 17, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a rotational rate comparator.
A fiber optic gyroscope with 3.times.3 coupler disclosed in U.S. Pat. No. 4,440,498 operates close to quadrature because of the 3.times.3 coupler, without need of a modulator. The further development of such a gyroscope and especially the gyroscope signal evaluation is described in Applied Optics, Volume 29, No. 36, pp. 53-60, Dec. 20, 1990. In the signal evaluation, the total and differential signals of the two photodiodes are used primarily. These photodiodes are located at the outputs of the 3.times.3 coupler as a direct extension of the fiber coil. To calculate the exact Sagnac phase, and hence the rotational rate, a plurality of factors and constants must be taken into account, so that an evaluating computer is necessary for evaluation. Nevertheless, fiber optic gyroscopes of this kind can now be manufactured so economically, and with sufficient accuracy, that they are suitable for use in missiles. Particularly in this case it has proven to be important to determine in a very short time whether a missile is exceeding a safety-critical rotational rate.
The object of the present invention is to provide a fiber optic gyroscope such as described above, which is both sturdy and economical, and which can fulfill this safety function.
These and other objects and advantages are achieved by the fiber optic gyro according to the invention, which includes an electrical circuit which is independent of the evaluating computer, and which includes logical elements that embody an algorithm for producing at least one output signal that depends on the rotational rate based on the photodiode signals. When such output signal exceeds at least one presettable limit the electrical circuit supplies an output signal.
The invention deliberately avoids using software-dependent data from the evaluating computer. Instead, it implements the algorithm via a fixed electrical circuit, so that a signal that depends on the rotational rate is generated directly from the photodiode signals. This rotational-rate-dependent signal can then also be compared with a given limiting value in a simple, software-independent manner.
For this purpose, a value that depends on the rotational rate, and which is relatively simple to form and largely free of other problems, is the quotient of the differential and total signals of the two photodiodes mentioned above. By suitable mathematical manipulation, an inequality can be developed for the limit consideration which utilizes, instead of a quotient, only additions and multiplications, and can be implemented simply with electrical adders, multipliers, and bistable flip-flops. As a result, it is possible to determine especially rapidly and reliably the rotational rate limiting values independently of the evaluating computer, so that even safety functions can be linked to it.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.